Adhesive compositions containing styrene/isobutylene copolymer

ABSTRACT

This invention discloses a new hot-melt, pressure-sensitive adhesive composition comprising a primary polymer consisting of a solid, homogeneous and essentially random copolymer of styrene and isobutylene having a number average molecular weight of from about 1,000 to about 4,000, a heterogeneity index of from about 1.50 to about 2.25 and a styrene content of from about 40 to about 90 weight percent, and a secondary polymer selected from the group consisting of a copolymer of ethylene and vinyl acetate, a copolymer of ethylene and an alkyl acrylate, a polyvinyl-alkyl ether, a terpolymer of ethylene, vinyl acetate and acrylic acid, and a terpolymer of ethylene, vinyl acetate and methacrylic acid.

Unite Sites atent Sheni'eld et all.

[72] Inventors: Richard S. Shenfeld; Frederick M. Musser;

Girish U. Kothari, all of Chicago, Ill.

[73] Assignee: Veisicol Chemical Corporation, Chicago,

Ill.

22 Filed: May13,1969

211 Appl.No.: 824,317

[51] lnLCl. [58] Fieid of Search [56] References Cited UNITED STATESPATENTS 3,386,929 6/l968 Brunei ..260/4 Battersby et al. ..260/ 889Tyran ..260/28.5

Primary Examinersamuel H. Blech Assistant Examiner-C. J. SeccuroAttorney-Robert J. Schwarz [57] ABSTRACT This invention discloses a newhot-melt, pressure-sensitive adhesive composition comprising a primarypolymer consisting of a solid, homogeneous and essentially randomcopolymer of styrene and isobutylene having a number average molecularweight of from about 1,000 to about 4,000, a heterogeneity index of fromabout L50 to about 2.25 and a styrene content of from about 40 to about90 weight percent, and a secondary polymer selected from the groupconsisting of a copolymer of ethylene and vinyl acetate, a copolymer ofethylene and an alkyl acrylate, a polyvinyl-alkyl ether, a terpolymer ofethylene, vinyl acetate and acrylic acid, and a terpolymer of ethylene,vinyl acetate and methacrylic acid.

7 Claims, No Drawings ADHESIVE COMPOSITIONS CONTAINHNGSTYRENE/ISOBUTYLENE COPOLYMER This invention relates to newpressure-sensitive adhesive compositions. More particularly, thisinvention relates to new hot-melt, pressure-sensitive adhesivecompositions containing as an essential component a novel copolymer ofstyrene and isobutylene.

Pressure-sensitive adhesives can be defined as adhesive materials whichadhere tenaciously upon application of only light pressure at ambienttemperatures, and which, in most instances, can be removed cleanly fromthe surface upon which they are applied. These pressure-sensitiveadhesives are widely used in a variety of applications, such as adhesivetapes, labels, decals and decorative papers, for sealing, masking,mending, fastening and decorative purposes.

Typically, pressure-sensitive adhesives consist of a tackifier resin, anelastomeric material and optionally such additives as plasticizers,fillers, antioxidants, extender resins, and the like. The tackifierresins which are commonly used vary greatly in their physical propertiesand chemical'makeup and include such materials as polyterpene resins,rosin esters, rosin derivatives, petroleum hydrocarbon resins,coumaroneindene resins, and the like. The elastomeric materials utilizedin pressuresensitive adhesives are the rubbery materials such asreclaimed rubber, natural rubber, styrene butadiene rubber,polyisobutylene or butyl rubber, or butadiene acrylonitrile rubber,polychloroprene rubber, polybutadiene rubber, polyisoprene rubber, andthe like.

in order to apply these pressure-sensitive adhesives onto a suitablesubstrate for final use, they are normally dissolved in an organicsolvent or, in some instances, they are emulsified to form an aqueouslatex. The solution or emulsion of the adhesive is then coated onto theparticular substrate desired and is evaporated leaving a solid filmpossessing pressure-sensitive properties.

Solvated adhesive systems, in spite of their preponderant use, possessnumerous disadvantages. For example, solvent base pressure-sensitiveadhesives are both fire and health hazards requiring explosionproofapplication equipment and suitable ventilation for the removal ofsolvent. Furthermore, the expedient removal of solvent from an adhesiveused in a commercial production line requires drying ovens which use upvaluable space and increase operating costs.

As a result it would be desirable to apply pressure-sensitive adhesivesonto the desired substrates without the use of liquid diluents orsolvents. In particular, it would be desirable to apply such adhesivesin the molten state as hot melts. The term hot melts is used in theadhesive industry to designate compositions which are solids at roomtemperature and which upon heating melt and flow freely for applicationto a substrate. The use of hot-melt adhesives, or adhesives applied inthe molten state without the use of solvents or liquid diluents,obviates many of the disadvantages inherent in solvent-based systems.Thus, fire hazards are virtually eliminated since hot melts contain noflammable components. Furthermore, hotmelt coating machinery isgenerally less expensive than machinery for coating solvent adhesivesand also requires less space since drying ovens are eliminated.

In response to the various advantages which can be realized through theuse of hot melts, the adhesive industry has recently attempted tosubstitute hot-melt adhesives for many of the applications wheresolvent-based adhesives have been used in the past. In the area ofpressure-sensitive adhesives, however, such attempts have met with onlylimited success since typical hot melts do not possesspressure-sensitive properties and pressure-sensitive adhesivecompositions generally decompose upon heating. The thermal instabilityof the majority of pressure-sensitive adhesives is due to theelastomeric constituents which they contain. The elastomeric materialswhich comprise both the natural and synthetic rubbers, while possessingthe properties useful for pressure-sensitive adhesives. are notthermoplastic and are therefore unsuited in hot melts.

Surprisingly, it has now been found that a pressure-sensitive adhesiveexhibiting excellent thermal stability can be prepared by using a novelcopolymer of styrene and isobutylene. More specifically, it has beenfound that a hot-melt pressure-sensitive adhesive composition can bereadily obtained by combining novel copolymers of styrene andisobutylene with a polymer selected from the group consisting of acopolymer of ethylene and vinyl acetate, a copolymer of ethylene andalkyl acrylate, a polyvinyl-alkyl ether, a terpolymer of ethylene, vinylacetate and acrylic acid, and a terpolymer of ethylene, vinyl acetateand methacrylic acid.

Thus, one embodiment of the present invention resides in a hot-meltpressure-sensitive adhesive composition which comprises a primarypolymer consisting of the copolymer of styrene and isobutylenehereinafter described and a secondary polymer selected from the groupconsisting of a copolymer of ethylene and vinyl acetate, a copolymer ofethylene and alkyl acrylate, a polyvinyl-alkyl ether, a terpolymer ofethylene, vinyl acetate and acrylic acid, and a terpolymer of ethylene,vinyl acetate and methacrylic acid.

The novel copolymers of styrene and isobutylene which are suitable forpreparing the hot-melt pressure-sensitive adhesive compositions of thisinvention are highly homogeneous and essentially random, solidcopolymers which have a low molecular weight, a broad molecular weightdistribution and a high weight content of styrene. These copolymers arefurther characterized by a combination of several other properties orcharacteristics such as a particular heat-softening point range, opticalclarity, thermal stability and a high degree of compatibility with otherpolymers and polymer systems.

The copolymers of styrene and isobutylene of this invention are capableof having a high content of styrene up to as high as 90 or, moreusually, 40 to weight percent. Yet, they are still highly homogeneous atsuch levels in that the copolymers are composed essentially of styreneand isobutylene copolymer units to the substantial exclusion of eitherstyrene or isobu tylene homopolymer units. The styrene content of thecopolymer ranges from as low as about 40 to as high as about weightpercent with the corresponding isobutylene content ranging from about 60to about l0 weight percent. The preferred copolymers, however, contain arelatively high content of styrene within the range of from about 40 toabout 70 weight percent styrene.

A high concentration of styrene is usually difficult to achieveespecially when copolymers of highly uniform composition are desiredconsisting essentially of styrene and isobutylene copolymer units to thesubstantial exclusion or absence of any styrene homopolymer units.Nevertheless, such uniform, highly homogeneous copolymers are readilyachieved in essentially quantitative yields when prepared according tothe preparational method as hereafter described.

The molecular weight of the copolymers of styrene and isobutylene ofthis invention in contradistinction to the typical copolymers of styreneand isobutylene is very low and moreover must be within a limited rangein order that the copolymers possess the desired set of properties forhot-melt pressure-sensitive adhesives. As used herein molecular weightis described both in terms of the weight average molecular weight M andthe number average molecular weight M However, unless specified to thecontrary, when used herein and in the appended claim, molecular weightwill mean the number average molecular weight K/T The significance ofthese conventional molecular weight terms as well as methods for theirdetermination are more fully described in the Structures of Polymers,M.l. Miller, Reinhold, New York, 1966. In general, the molecular weightof the copolymers of styrene and isobutylene of this invention can rangefrom about 1,000 to about 4,000. A more limited molecular weight range,however, which is readily achieved by utilization of the preparationalmethod of this invention is preferred and ranges from about 1,200 to3,500. This latter limited range is particularly preferred in that thecopolymers having this low molecular weight range are especiallysuitable for use in hot-melt pressure-sensitive adhesives.

In addition to a limited, low molecular weight range. the copolymersofstyrene and isobutylene of this invention have a broad molecularweight distribution. This distribution of the molecular weights of thecopolymer may be described conventionally in terms of a heterogeneityindex which is defined as the ratio of the weight average molecularweight to the number average molecular weight, M /lfi Usually, theheterogeneity index, Fli /17! for the copolymers can range from about1.50 to about 2.25. Typically, however, for copolymers having thepreferred molecular weight, the heterogeneity index ranges from about1.65 to about 2. 15.

As indicated, the copolymers of styrene and isobutylene of thisinvention are characterized by a high degree of randomness, that is, thecopolymers consist essentially of basic repeating units of the followingformula:

wherein m and n are integers from 1 to about 15, and the styrene andisobutylene moieties are distributed in an essentially random manner.Furthermore, the above basic repeating unit is located along the polymerchain in an essentially random distribution. The total number ofdescribed basic repeat ing units in the copolymer is such that thenumber average molecular weight is from about 1,000 to about 4,000. Thusthe polymers of styrene and isobutylene of this invention do not containlong sequences of styrene or isobutylene units, not do they contain longsequences of alternating styrene and isobutylene units. Thisdistinguishes these copolymers from bloclttype copolymers whichessentially contain long sequences of styrene and isobutylene unitsalong their molecular chain. It also distinguishes the copolymers from agraft-type copolymer where repeating units of either styrene orisobutylene are attached to a backbone chain of the other. In additionto indicating the random nature of the copolymer of this invention theabove formula also serves to illustrate the specific nature of thecopolymer in that there are substantially no ring alkylated styreneresidues in the polymer arising from an in situ al' kylation of thestyrene by the isobutylene and further that the polymerization of theisobutylene unit takes place so that there are two methyl groups and notonly one perpendicular to the molecular chain.

The styrene-isobutylene copolymers of this invention, as indicated, arenormally solid materials and have relatively high heat-softening points.As measured by the ring and ball method, the heat-softening point of thecopolymers can range from about 125 F. to about 225 F. A more limitedrange of from about 130 F. to about 225 F. and especially from about Mto 205 F. is preferred, however, for maximizing the usefulness of thecopolymers in applications as hot-melt pressuresensitive adhesives. Afurther and important characterizing property of the copolymers of thisinvention is that they have good thermal stability and are stableagainst chemical decomposition at temperatures above 350 C.

While the copolymers of styrene and isobutylene of this invention can bedefined by reference to the above characterizing properties such asmolecular weight, molecular weight distribution, randomness andcompositional homogeneity, as well as softening points, such propertiesare a function of or interrelated to their specific method ofpreparation. Ac cordingly, the copolymers can, in addition to suchproperties, also be defined or characterized by references to suchmethod of preparation. in preparing the copolymers according to thisinvention, a specific preparational method should be utilized in orderthat all of the above-described properties be obtained especially in thepreferred ranges. Utilization of such method, moreover, not only permitsthe obtainment of the desired copolymers, but in addition achieves suchresult with almost theoretical conversions and in a particularconvenient and desirable industrial manner. This preparational methodinvolves an interrelated combination of processing features whichbasically comprises an elevated polymerization temperature, a particularcatalyst system and a certain mode of conducting the polymerizationreaction. This method is effected, in general, by gradually bringing thestyrene and isobutylene into reactive contact, in the presence ofahydrocarbon polymerization solvent, with a catalyst system of a primarycatalyst and a cocatalyst while maintaining an elevated polymerizationtemperature.

The catalyst system which is utilized in the preparation is composed ofa primary catalyst and a cocatalyst which are maintained in a specific,relative proportion, Both the selection of the primary catalyst and thecocatalyst and their relative proportions in the catalyst system areimportant to the success of the method in producing high yields ofcopolymers having all of the ultimately desired properties. The primarycatalyst can consist of at least one alkyl aluminum dihalide whereinthe'allryl portion can have from one to about five carbon atomsincluding, for example, such groups as methyl, ethyl, propyl and butyland the halide portion can be a halogen atom having an atomic weightwithin the range of from about 35 to about including, for example,chlorine and bromine. Of the various alkyl aluminum dihalides which canbe employed, the preferred primary catalyst is ethyl aluminumdichloride.

The cocatalyst utilized in combination with the primary catalyst in thecatalyst system comprises at least one material selected from the groupconsisting of water, an alkyl halide, a hydrogen halide or an alcohol.Examples of these cocatalysts include alcohols such as allaanols havingfrom one to about five carbon atoms in the alkyl portion of themolecule, such as ethyl alcohol, propyl alcohol, tertiary butyl alcoholor mixtures thereof; secondary or tertiary alkyl halides where the alkylportion contains from about three to about five carbon atoms and wherethe halide portions is the same as defined above, such as butylchloride, propyl chloride or pentyl chloride; or a hydrogen halide suchas hydrogen chloride or hydrogen bromide. Of the various catalysts whichcan be employed, an alkanol such as tertiary butyl alcohol or an alkylhalide such as tertiary butyl chloride and especially water arepreferred and particularly when used in combination with the preferredprimary catalyst, ethyl aluminum dichloride.

As indicated, the relative proportions or ratio of the cocatalyst tocatalyst in the catalyst system is important in achieving copolymershaving the desired set of properties. While this ratio can varydepending upon such factors as the particular catalyst and cocatalystused, it should be maintained within certain limits if copolymers of thedesired properties such as molecular weight and molecular weightdistribution are to be achieved. Generally, the cocatalyst should bepresent in the catalyst system within a range of from about 2 to 30 molpercent based upon the mols of the primary catalyst present. A morelimited range of from about 2.5 to 15 or about 5 to about 10 mol percentis preferred for such cocatalysts as water and particularly when usedwith the preferred, primary catalyst, ethyl aluminum dichloride. Thequantity of the primary catalyst used in the catalyst system which inturn determines the quantity of cocatalyst can also be varied. Theparticular amount used is dependent upon such factors as the particularprimary catalyst, the cocatalyst and the polymerization temperature.Generally, the quantity ofthe primary catalyst can range from about.0.20 to about 1.5 weight percent based upon the combined weight of thestyrene and isobutylene monomers. A more limited range of about 0.25 to1.2 or about 0.4 to about 1.0 is preferred, however, when employingcatalyst systems containing ethyl aluminum dichloride in combinationwith cocatalysts such as water, alkyl halides or alkanols.

In preparing the catalyst system, the cocatalyst and the primarycatalyst can be admixed in the desired ratio prior to thepolymerization. More preferably, it can be prepared in the presence ofthe solvent just prior to polymerization by simply adding theappropriate quantities of catalyst and cocatalyst to the solvent withmixing. The primary catalyst itself can also be prepared in situ duringor just prior to the polymerization by combining the necessary materialsto form the desired alkyl aluminum dihalide. For example, aluminumchloride can be admixed with diethyl aluminum chloride in theappropriate proportion to form the active, preferred ethyl aluminumdichloride catalyst in situ. Generally, however, it is preferable to addthe primary catalyst as a relatively pure compound to the solventtogether with the cocatalyst just prior to the polymerization.

The temperature utilized in effecting the polymerization, as indicated,is unusually high for the polymerization of styrene and isobutylene toform normally solid copolymers. Nevertheless, this high temperature is anovel and important feature of the preparational method of the copolymerof styrene and isobutylene ofthis invention. Utilization of such hightemperature in combination with the catalyst system as well as with themode of conducting the polymerization permits the attainment of theunique copolymers of this invention having all of the desirableproperties such as low molecular weight and a broad molecular weightdistribution. Moreover, employment of this elevated temperature allowsthe polymerization to be conducted in a highly convenient and desirablemanner in that the extensive cooling, critical in effecting the lowtemperature polymerization of styrene and isobutylene, is necessary. Thepolymerization temperature can range from about to about 50 C. with thespecific temperature utilized within this range being dependent uponsuch factors as the catalyst system employed, the solvent and theultimately desired properties of the copolymer. Usually, however, a morelimited temperature range is preferred of from about to about 25 C. orabout C. especially when preparing the preferred class of copolymersaccording to this invention.

The hydrocarbon solvent used to effect the polymerization can include awide class of hydrocarbon polymerization solvents. The particularsolvent employed in the polymerization, however, will affect theultimate properties of the copolymer produced. Accordingly, it isimportant to select a solvent or combination of solvents which providesa copolymer having the ultimately desired properties. The solvents whichcan be used individually or in combination include aliphatics such asalkanes containing from about six to about 10 carbon atoms per moleculesuch as hexane or heptane and aromatics such as benzene or alkylatedbenzenes such as toluene, xylene or ethyl benzene. Of the varioussolvents which can be utilized, preferred solvents are alkanes such ashexane or heptane or mixtures thereof. The quantity of solvent employedcan be varied but there should at least be a quantity ofsolvent presentsufficient to provide a readily stirrable reaction mixture. Typicallywhen using solvents such as hexane this amount ranges from about 0.5 toabout 2 weight parts or preferably equal weight parts of solvent per oneweight part of the combined styrene and isobutylene charge.

In conducting the preparational method, another important processingfeature in combination with the features of the catalyst system andelevated polymerization temperature is the particular mode used to bringthe styrene and isobutylene into reactive contact with the catalystsystem. It is most important that the styrene and isobutylene begradually contacted with the catalyst system in the presence of thesolvent if the copolymers of the desired properties are to be achieved.This contacting is preferably effected by gradually adding both thestyrene and isobutylene to the solvent containing the catalyst systemwhile maintaining the desired polymerization temperature. In graduallyadding the styrene and isobutylene, preferably admixed in a single feedstream, the time required to complete the addition will vary dependingupon such factors as the particular catalyst system and thepolymerization temperature utilized and to a lesser degree upon thescale of the reaction. Generally, however, the styrene and isobutyleneshould be added at a rate adjusted so that they are substantiallycompletely polymerized upon contact with the catalyst system leavingsubstantially no unreacted monomer in the reaction mixture. Typically,this addition time can range from about 0.10 to 2 hours with additiontimes of from about 0.5 to 1.5 or about 1.0 hours being preferred formaximizing the desired properties of the copolymers produced. The chargestream of styrene and isobutylene gradually added to the mixture ofsolvent and catalyst system can contain styrene in an amount of fromabout 40 to weight percent. However, when preparing the preferredcopolymers according to this invention, the charge contains styrene inan amount ranging from about 40 to 70 weight percent.

The polymerization method for preparing the copolymers of styrene andisobutylene of this invention can be conducted in a batch, semibatch orcontinuous operation. A batch operation is usually suitable, however,and one illustrative procedure involves gradually adding a single streamofstyrene and isobutylene monomers, admixed in the desired weight ratio,to the stirred solvent containing the appropriate catalyst system. Thegradual addition of the styrene and isobutylene is regulated so thatsubstantially all of the styrene and isobu tylene are polymerized uponcontact with the catalyst system leaving substantially no unreactedmonomer in the reaction mixture. During the addition, the temperature ofthe exothermic reaction is maintained within the desired range byutilizing appropriate cooling means. When the addition of the monomersis complete, the copolymer product can then, if desired, be recoveredfrom the reaction mixture. It is generally desirable, however, to leavethe copolymer in the reaction mixture in the presence of the catalystsystem at the polymerization temperature for a residence periodsufficient to insure total, uniform polymerization. The length of thisresidence period can range from only a few minutes to 1 hour or more.Typically, residence periods ranging from about 0.25 to 3 hours aresufficient with about 0.75 to 2.5 or about l hour usually beingpreferred. After the copolymer has been in contact with the catalystsystem for a sufficient residence period it can be removed from thereaction mixture and purified according to several different procedures.Advantageously, the removal procedure involves first eliminating thecatalyst system from the reaction mixture by adding a solid adsorbant toadsorb the catalyst and the solids can then be eliminated as a solidfiltrate. Alternatively acidic or basic materials can be added to formwater-soluble adducts of the catalyst. Such ad ducts can then be removedby water washing of the reaction mixture. After the catalyst system hasbeen eliminated by one of the above procedures or a combination thereof,the solvent and any impurities formed in the polymerization can bereadily removed from the reaction mixture by distillation at reducedpressure, leaving the desired copolymer in high yield.

The following examples are offered to illustrate the novel copolymers ofstyrene and isobutylene of this invention and the method for theirpreparation. They are not intended, however, to limit the invention tothe particular copolymers or preparational procedures.

EXAMPLE 1 A series of copolymers of styrene and isobutylene wereprepared according to this invention by the following procedures.

Anhydrous hexane in an amount substantially equal in weight to thecombined weight of the styrene and isobutylene to be polymerized wascharged under a nitrogen atmosphere to a polymerization vessel equippedwith an addition funnel, stirring and cooling means and an overheadcondenser. The catalyst system was added by first charging a cocatalystto the hexane with stirring followed by the addition of the primarycatalyst consisting of freshly prepared substantially pure ethylaluminum dichloride contained in heptane or hexane. After stirring for aperiod of time sufficient to insure adequate formation and dispersion ofthe catalyst system in the hexane, a premixed charge stream of styreneand isobutylene adjusted to the desired weight ratio was gradually addedover a controlled addition time via the addition funnel whilemaintaining the desired polymerization temperature by cooling. After theaddition was complete, the stirring was continued for a residencecopolymer chemically decomposes under application of heat, wasdetermined using Differential Scanning Calorimetry techniques. Theheat-softening point was obtained by the Ring and Ball Method of ASTME28-58T.

TABLE II Weight Number Heat average average Hetero- Soit Thermalmolecular molecular genelty fining deglw weight Weight index, p'oimydam), Copolymer N0. MW n Hwy/ n F. Appearance 2, 100 1. 71 Clear, waterwhite, 2, 450 1. 84 D0. 1,750 1. 01 Do. 2, 000 1. 72 D0. 2, 075 1. 84Do. 2, 100 1. 84 D0. 2, 000 2. 12 Do. 2, 000 1. 03 D0. 2, 150 1 91 D0.2, 150 1 91 D0. 2, 100 1. 90 Do. 2, 100 1. 98 Do. 2, 150 1. 86 Do. 2,650 1. 71 2, 850 1. 80 Do. 2, 225 1. 95 Do. 2, 275 2. 07 D0. 2, 705 2.01 D0. 1, 250 2.68 Clear, yellowish.

2, 200 2,0 7 215 401 Clear, water white. 2, 700 1. 65) 205 300 D0. 2,450 1. 98 207 400 Do, 2, 400 1. 93 207 402 D0. 2, 400 1. 90 200 382 Do.2, 325 1. 02 206 367 Slight haze, water white. 2, 400 2. 2, 125 1. 87367 Slight haze, water white. 750 1. 90 402 Clear, slight yellow.

period sufficient to insure total and complete polymerization. Thecatalyst system was then removed by adding ethyl alcohol and solidcalcium hydroxide to neutralize the catalyst system followed by addingan acid-acting clay to adsorb the neutraltyrene and isobutylene of thisinvention the following examized catalyst residue. After filtering theclay from the reaction mixture, the solvent and any side productsproduced during polymerization were removed by distillation underreduced pressure of about 1 mm. Hg at a temperature of about 225 C.

The polymerization conditions employed for the preparation of thecopolymers are summarized in the following Table l and the properties ofthese copolymers are summarized in Table II.

In Table II, the molecular weights reported were determined using GelPermeation Chromatography techniques employing absolute molecular weightstandards determined by Vapor Pressure Osmometry techniques. The thermaldegradation temperature, that is the temperature at which the EXAMPLE 2To demonstrate the random nature of the copolymers of ple is cited. Acopolymer was degraded using lauryl peroxide and the degradationproducts were analyzed according to the following procedure.

About grams of hexane and 4.0 grams of lauryl peroxide were charged toasealed flask together with about 50 grams of copolymer No. 27 ofExample 1. This copolymer analyzed by nuclear magnetic resonancespectroscopy was composed of 77.87 weight percent styrene. The mixturewas heated at 70" C. for about 20 hours. During this period samples ofthe mixture were taken at intervals of l, 2, 4 and 20 hours. Theindividual samples were filtered through a column of an acidacting clayto remove acidic compounds and the filtrate was TAB LE I Polym- Styrene/erizaisobu- (Jo-catalyst tion Addi- Resitylene Primary temtion denceCopolymonomer catalyst, M01 peratime, tlme, lner weight weight perture,miumin- Yield Ne. ratio pereent Type cent 2 C. utes utes percent50/50 1. 0 H20 20 20 70 96 50/50 0. 5 1120 5-10 20 (i0 180 06 50/50 0. 5H20 10 10-32 60 00 06. 7 50/50 0. 5 H20 7 20 60 60 02. 0 50/50 0. 5 H207 20 00 60 04. 5 50/50 0. 5 H20 5 20 40 60 J6. 0 60/40 0. 5 H20 5 20 3060 95 60/40 0. 5 H20 5 20 30 60 60/40 0.5 H20 10 20 60 89 60/40 0. 5 H205 20 65 61 65/35 0. 5 H20 5 20 60 60 94. 2 65/35 0. 5 H20 5 20 60 60 9465/35 0.5 H20 5 20 30 60 97. 5 /30 0. 25 H20 10 20 60 60 96 70/30 0. 5H20 5 20 50 60 95 70/30 0. 5 H20 5 20 30 60 92. 5 70/ 30 0. 5 H20 3 0 6060 93. 5 70/30 0. 5 H20 5 20 60 60 95 /25 1.0 t-Bu Cl 20 20-25 65 60 9275/25 0. 25 t-Bu OH 20 0-25 25 60 98. 6 75/25 1.0 H10 10 20 30 60 8375/25 0.5 H20 5 19-22 27 60 75/25 1.0 H 0 2. 5 19-23 29 60 75/25 1.0 H2010 19-20 30 60 97 75/25 0. 5 H2O 19-20 30 99 75/25 0.25 1120 10 18-23 30120 90 75/25 0.5 H20 2 5 19-24 35 120 80/20 0. 5 H20 7 5 20 23 60 120 9680/20 0.5 H20 5 19-21 60 120 1 Based upon combined monomer weight. 2Based upon mols primary catalyst.

distilled at l to 4 mm. Hg pressure to a pot temperature of 225 C. Thedistilled samples were than analyzed by infrared spectroscopy forstructural characteristics. The infrared spectra of all of the sampleswere substantially the same. This indicated that the copolymer isessentially random in nature and has no block copolymer characteristicsof large blocks of polystyrene or polyisobutylene or any graft polymercharacteristics of substantial chains of either polystyrene orpolyisobutylene grafted to a backbone of the other.

As indicated the secondary polymer with which the copolymers ofstyreneand isobutylene of this invention'can be combined to form a hot-meltpressure-sensitive adhesive composition is selected from the groupconsisting of a copolymer of ethylene and vinyl acetate, a copolymer ofethylene and an alkyl acrylate, a polyvinyl-alkyl ether, a terpolymer ofethylene, vinyl acetate and acrylic acid, and a terpolymer of ethylene,vinyl acetate and methacrylic acid. Combinations of these polymers canalso be utilized in the adhesive composi tions of this invention toachieve a specific balance of properties.

All ofthe secondary polymers are well known in the art and a number ofthem are sold commercially under various trade names. While all of thesepolymers can be utilized in the compositions of this invention, the useof polymers having certain ranges of properties is preferred.

Preferred copolymers of ethylene and vinyl acetate are those having asoftening point (ring and ball method) of from about 180 F. to about 390F., a percent vinyl acetate content of from about to about 55 percent byweight and a melt index (ASTM Method D 1238) of from about 0.5 to about500, and most preferred copolymers of ethylene and vinyl acetate have amelt index of from about 100 to about 300 and a percent vinyl acetatecontent of from about 24 to about 42 percent. Often two or more gradesof such polymers can be blended to obtain a mixture having usefulproperties beyond those ofthe individual components.

The preferred copolymers of ethylene and alkyl acrylates which can becombined with the copolymers of styrene and isobutylene of thisinvention to form the novel adhesive compositions have a melt index offrom about 2 to about 300 and an alkyl acrylate content which rangesfrom about 15 to about 40 weight percent. Exemplary suitable copolymersof ethylene and alkyl acrylates are copolymers of ethylene and ethylacrylate, copolymers of ethylene and propyl acrylate, copolymers ofethylene and isobutyl acrylate, and the like.

The polyvinyl-alkyl ether resins which are most useful for preparing thecompositions of this invention are polyvinylmethyl ether,polyvinyl-ethyl ether and polyvinyl-isobutyl ether. The preferredpolyvinyl-alkyl ethers for the purpose of this invention have a meltindex of from about to about 300.

The terpolymers of ethylene, vinyl acetate and acrylic acid, and ofethylene, vinyl acetate and methacrylic acid which can be suitably usedin the pressure-sensitive adhesive compositions of the present inventionare fully described in US. Pat.

To obtain hot-melt pressure-sensitive adhesive compositions of thepresent invention the copolymers of styrene and isobutylene are combinedwith the secondary polymers enumerated above in certain proportions.Generally the compositions can comprise of from about 20 to about 80weight percent of the copolymer of styrene and isobutylene and fromabout 20 to about 80 weight percent of the secondary polymer. In apreferred embodiment of the present invention the adhesive compositioncomprises from about 40 to about 65 weight percent of the copolymer ofstyrene and isobutylene and from about 35 to about weight percent of thesecondary polymer. The particular proportions within the above rangescan vary with the specific end use ofthe composition.

The basic hot-melt, pressure-sensitive adhesive composition of thisinvention can be modified with various materials to result incompositions which exhibit additional useful properties or decreasetheir cost. These materials which comprise plasticizers, mineralfillers, pigments, antioxidants, UV-absorbers and resin extenders arenot critical to the present invention but are regularly used in theadhesive art to tailor the composition to a specific need.

The use of plasticizers in the compositions of the present invention canbe desirable and will often enhance the machinability of the product byadjusting its viscosity at those temperatures at which the adhesivecompositions are applied to a substrate. The incorporation ofplasticizers into the adhesive composition can improve its aggressivetack or quick-stick" property. Exemplary plasticizers which are used inthe art and which can be suitably utilized in the compositions of thepresent invention are petrolatum, mineral oil, chlorinated parafins,diisobutyl phthalate, tricresyl phosphate, dioctyl phthalate, propyleneglycol dibenzoate, chlorinated aromatic compounds, lower aliphaticesters of adipic acid, lower aliphatic esters of sebacic acid, and thelike. The amount of plasticizer which can be used in the adhesivecompositions can range up to about 20 percent by weight of the totalcomposition.

Mineral fillers are commonly used in adhesive compositions as extendersto improve the economics of the formulation and often impart creepresistance to it. When used, these fillers can comprise up to about 30percent by weight of the total formulation. Fillers which can be used inthe compositions of this invention are exemplified by calcium carbonate,barium sulfate, silica, talc, china clay and bentonite.

Antioxidants and UV-absorbers can be incorporated into the adhesivecompositions of this invention to improve their aging characteristics.Useful antioxidants and UV-absorbers are butylated hydroxy toluene,butylated hydroxy anisole, diphenolic hindered antioxidants, and thelike.

The adhesive compositions of this invention can also be modified orextended with polymeric materials, other than those required asessential ingredients, having a softening point (ring and ball method)of from about F. to about 350 F. and having a melt index of from about 2to about 300. These materials can be hydrocarbon resins such as arecommonly prepared from a dripolene stream, atactic polypropylene andpolyethylene or resins such as rosin derivatives, terpene resinsincluding alphaand beta-pinene resins, and the like. The use of suchextending resins is common practice in the adhesive art, especially forthe purpose of lowering formulation costs or modifying the formulationto fit specific needs. Extending resins can be used to replace up toabout 50 percent by weight of the copolymer of ethylene and vinylacetate, the copolymer of ethylene and alkyl acrylate, thepolyvinyl-alkyl ether, the terpolymer of ethylene, vinyl acetate andacrylic acid, or the terpolymer of ethylene, vinyl acetate andmethacrylic acid, or 40 percent by weight of the total adhesivecomposition.

The hot-melt, pressure-sensitive adhesive compositions of the presentinvention can be readily prepared by mixing the ingredients attemperatures from about 200 to 400 F. in conventional formulatingequipment. A typical preparation comprises charging the copolymer ofstyrene and isobutylene into a suitable formulating vessel equipped withheating and stirring means. This resin is then heated to a temperaturewhich allows blending with the secondary resin in the molten state. Theplasticizer is then added, if used, to facilitate stirring. After thedesired temperature is reached, which will usually range from about 250to about 350 F., the secondary resin can be added at a sufficiently slowrate that will not impair stirring. Other additives, when used, can beadded at this time and heating and stirring are continued until ahomogeneous blend is obtained. This composition can then be useddirectly for coating onto a desired substrate as a pressure-sensitiveadhesive or can be placed into storage containers and cooled for futureuse.

For application to a substrate the adhesive is heated to a temperaturein the range of from 250 to 350 F. Generally the lowest temperature thatproduces the viscosity desired and suitable for the particularapplication of the adhesive is employed.

The hot-melt, pressure-sensitive adhesive compositions of the presentinvention and their preparation are more specifically illustrated by thefollowing examples.

EXAMPLE 3 A copolymer of styrene and isobutylene (80 grams) prepared inaccordance with the procedures detailed in Example l and having astyrene/isobutylene monomer weight ratio of 50/50 was placed into astainless steel cup and was heated with stirring to a temperature ofabout 330 F. A copolymer of ethylene and vinyl acetate (20 grams) havinga melt index of from 22 to 28 and a vinyl acetate content of from 24 toabout 32 percent by weight was incrementally added over a period ofabout 10 minutes. Heating and stirring were continued until ahomogeneous composition was obtained. The composition was then appliedas a thin coating to a flexible polyester sheet (Mylar, l.0 mil) and wasallowed to cool. The resulting pressure-sensitive adhesive tape was thensubjected to certain tests to demonstrate the utility of the hot-melt,pressure-sensitive composition of this invention. The results aresummarized in Table lll.

EXAMPLE 4 A copolymer of styrene and isobutylene (55 grams) prepared inaccordance with the procedures detailed in Example l and having astyrene/isobutylene monomer weight ratio of 50/50 was placed into astainless steel cup and was heated, with stirring, to a temperature ofabout 340 F. Petrolatum 10 grams) and a mixture of copolymers ofethylene and vinyl acetate, 15 grams and 20 grams of copolymers having apercent vinyl acetate content of 27 to 29 and 39 to 42 respectively andhaving a melt index of 335 to 365 and 45 to 70 respectively, were thenincrementally added over a period of about 20 minutes. Heating andstirring were continued until a homogeneous mixture was obtained. Thecomposition was then coated onto a flexible polyester sheet for testinggiven the results as shown in Table Ill.

EXAMPLE 5 The copolymer of styrene and isobutylene (40 grams) preparedin accordance with the procedures described in Example l and having astyrene/isobutylene ratio of 50/50 was placed in a stainless steel cupand was heated, with stirring, to a temperature of about 340 F. Acopolymer of ethylene and isobutyl acrylate (50 grams) having anisobutyl acrylate monomer content ofabout 20 weight percent and a meltindex of about 250 (commercially sold as Zetafax-l278 by the DowChemical Company) and mineral oil grams) were then added over a periodof several minutes. Heating and stirring were continued until ahomogeneous mixture was obtained. This mixture was then coated onto aflexible polyester sheet for testing. The results are given in TableIII.

A variety of additional hot-melt, pressure-sensitive adhesivecompositions were prepared in the manner described in the foregoingexamples. In the following examples are given the essential ingredientsin parts by weight which were utilized to form useful compositions bythe procedures heretofore described. For the sake of brevity thecopolymers of styrene and isobutylene of this invention are designatedas $1 8.

EXAMPLE 6 SIB copolymer 20 (50/50 styrene/isobutylene ratio) Ethylenevinyl acetate copolymer 80 .(Ultrttthene 664-X) A product oflLS,Industrial Chemicals Company (Gantrez M-0'94) A product ofGeneralAniline and Film Corporation EXAMPLE 9 SIB copolymer 55 (SO/50styrene/isobutylene ratio) Ethylene vinyl acetate copolymer l5 (Elvax210) Ethylene vinyl acetate copolymer 20 (Elvax 40) Propylene glycoldibenzoate 10 "A product ofE. l. Du Pont De Nemours and Company EXAMPLEl0 SIB copolymer 70 (SO/5O styrene/isobutylene ratio) Polyvinyl methylether 30 (Gantrez M-O94) EXAMPLE 1 1 SIB copolymer 60 (40/60styrene/isobutylene ratio) Ethylene vinyl acetate copolymer 35 (Elvax220) Propylene glycol dibenzoate 5 EXAMPLE l2 SIB copolymer 4O(copolymer No. ll from Table ll) Ethylene vinyl acetate copolymer 3U(Elvax 40) Ethylene isobutyl acrylate copolymer 20 (Zetafax I370)Petrolatum l0 EXAMPLE l3 SIB copolymer 20 (copolymer No. l4 from Tablell) Polyvinylisubutyl ether 65 (Gantrcz 8-201) Talc l5 EXAMPLE l4 SIBcopolymer 50 (copolymer No. 1 from Table ll) Polyvinyl-methyl ether 30(Lutonal M40) Al ha-pinene resin 20 A product of BASF CorporationEXAMPLE l5 SIB copolymer 6U (copolymer No. I from Table ll)Polyvinyl-ethyl ether 20 (Lutonal A25) Ethylene vinyl acetate copolymer20 (Elvax 2l0) EXAMPLE l6 SlB copolymer 55 (copolymer No. I from Tablell) Ethylene isobutyl acrylate copolymer 30 (Zetafax I278)Polyvinyl-isobutyl ether l0 (Gantrez B-ZOI) Dioctyl phthalate 5 EXAMPLEl7 SIB copolymer 6O (copolymer No. I from Table ll) Ethylene. vinylacetate and acrylic acid terpolymer 30 Petrolatum l0 EXAMPLE l8 SIBcopolymer 60 (copolymer No. I from Table ll) Ethylene. vinyl acetate andmethacrylic acid terpolymer 3O Petrolatum l0 TABLE III Peel Shear FingerAdhesion Adhesion Test Compound Tack I g./in. hours Product of Example 3good 260 168+ Product of Example 4 good 800 60 Product of Example 5 fair350 6.5 Product of Example 6 fair 250 103+ Product of Example 7 good2000+ 2 Product of Example 8 good I I20 1.5 Product of Example 9 good 3I0 24 Product of Example 10 good 3 Finger tack is a simple preliminarytest to determine the aggressive tack of the adhesive compositions. Thistest is performed by lightly touching the adhesive mass and rating thetenacity of the produced bond on a basis of poor, fair and good.

The peel adhesion and shear adhesion tests employed were conductedaccording the standardized tests promulgated by the Pressure SensitiveTape Council, Glenview, Illinois, U. S. A.

We claim:

1. A hot-melt, pressure-sensitive adhesive composition consistingsubstantially of a. from about 20 to about 80 percent by weight of asolid homogeneous and essentially random copolymer of styrene andisobutylene having a number average molecular weight of from about 1,000to about 4,000, a heterogeneity index of from about 1.50 to about 2.25and a styrene content of from about 40 to about 90 weight percent,

b. from about 20 to about 80 percent by weight of at least one polymerselected from thegroup consisting of (1) a copolymer of ethylene andvinyl acetate having a softening point of from about 180 F. to about 390F., a percent vinyl acetate content of from about 15 to about 55 weightpercent, and a melt index of from about 0.5 to about 500, (2) acopolymer of ethylene and an alkyl acrylate having an alkyl acrylatecontent of from about 15 to about 40 weight percent and a melt indexfrom about 2 to about 300, and'( 3) a terpolymer of ethylene, vinylacetate and acrylic or methacrylic acid,

c. from to about 20 percent by weight of the total composition ofplasticizer,

2. The composition of claim 1, wherein the copolymer (a) has a numberaverage molecular weight of from about 1,200 to about 3,500 and a ringand ball softening point of from about 140 F. to about 205 F.

3. The composition of claim 1, wherein the polymer (b) is the copolymerof ethylene and vinyl acetate.

4. The composition of claim 1, wherein the polymer (b) is the copolymerof ethylene and an alkyl acrylate.

5. The composition of claim 1, wherein the polymer (1;) is theterpolymer of ethylene, vinyl acetate and acrylic or methacrylic acid. 7

6. The composition of claim 4, wherein the polymer is a copolymer ofethylene and isobutyl acrylate.

7. The composition of claim 1 wherein the copolymer of styrene andisobutylene is prepared by gradually contacting styrene and isobutylenein a proportion of from about 40 to weight percent styrene at apolymerization temperature of from about 10 C. to about 50 C. in thepresence of a hydrocarbon solvent with a catalyst system of an alkylaluminum dihalide primary catalyst and at least one cocatalyst selectedfrom the group consisting of water, an alcohol, an alkyl halide and ahydrogen halide, maintaining the styrene and isobutylene in reactivecontact with the catalyst system for a time sufficient to insurecomplete polymerization.

2. The composition of claim 1, wherein the copolymer (a) has a number average molecular weight of from about 1,200 to about 3, 500 and a ring and ball softening point of from about 140* F. to about 205* F.
 3. The composition of claim 1, wherein the polymer (b) is the copolymer of ethylene and vinyl acetate.
 4. The composition of claim 1, wherein the polymer (b) is the copolymer of ethylene and an alkyl acrylate.
 5. The composition of claim 1, wherein the polymer (b) is the terpolymer of ethylene, vinyl acetate and acrylic or methacrylic acid.
 6. The composition of claim 4, wherein the polymer is a copolymer of ethylene and isobutyl acrylate.
 7. The composition of claim 1 wherein the copolymer of styrene and isobutylene is prepared by gradually contacting styrene and isobutylene in a proportion of from about 40 to 90 weight percent styrene at a polymerization temperature of from about 10* C. to about 50* C. in the presence of a hydrocarbon solvent with a catalyst system of an alkyl aluminum dihalide primary catalyst and at least one cocatalyst selected from the group consisting of water, an alcohol, an alkyl halide and a hydrogen halide, maintaining the styrene and isobutylene in reactive contact with the catalyst system for a time sufficient to insure complete polymerization.
 300. 